Ozone in the troposphere

Trees and shrubs contain a group of fragrant compounds called terpenes. The simplest terpene is isoprene. All other terpenes are built around carbon skeletons constructed from one or more isoprene units. Plants emit terpenes into the atmosphere, as anyone who has walked in a pine or eucalyptus forest will have noticed. The possible effect of terpenes on the concentration of ozone in the troposphere has been the subject of much debate and has led to careful measurements of rates of reaction with ozone. 

Ultraviolet photolysis of ozone (there is a small background level of ozone in the troposphere as a result of downward transport from the stratosphere) ... 

Nitrous oxide (N2O) is an important greenhonse gas with a radiative forcing effect 310 times that of CO2 and a lifetime in the troposphere of approximately 120 years. Part of the N2O is converted to NO in the stratosphere, and so contributes to depletion of ozone. Nitric oxide (NO) is very reactive in the atmosphere and has a lifetime of only 1-10 days. It contribntes to acidification and to reactions leading to the formation of ozone in the troposphere, and so also to global warming. 

Nitrogen oxides (NO ) are formed during the combustion at high temperature of fossil fuels and of biomasses and are blamed for the production of acid rain, the formation of ozone in the troposphere and of secondary particulate matter and for causing a reduction in breathing functionality and damage to the cardio-circulatory system in humans. 

These alkyl nitrate compounds have been measured in the troposphere and constituted about 1.5% of the total odd nitrogen budget at a rural eastern U.S. site (19). Reaction 16a competes with the oxidation of NO by ozone in the troposphere. 

In this study we will present aspects of STE in relation with the budget and concentrations of ozone in the troposphere, specifically in the Northern Hemisphere. Firstly, we present ozone observations in the tropopause region from the measurement campaign MOZAIC, and discuss their correlation with potential vorticity. The results have been used to improve the parameterization of stratospheric ozone in a coupled tropospheric chemistry - general circulation model. We will show examples of the performance of the model regarding the simulation of ozone in the tropopause region, and present the simulated seasonality of cross-tropopause ozone transport in relation to other tropospheric ozone sources and sinks. Finally, we will examine and compare the influence of cross-tropopause transports to surface ozone concentrations for simulations with contemporary, pre-industrial, and future emission scenarios. 

Roelofs, G.J., Lelieveld, J., and van Dorland, R. (1997) A three-dimensional chemistry/general circulation model simulation of anthropogenically derived ozone in the troposphere and its radiative climate forcing, J. Geophys. Res. 102,23389-23401. 

Increases of ozone in the troposphere are mainly a result of increases in NOx, which is an important agent in tropospheric ozone production. In the lower tropical stratosphere, another factor is the increase in the photolysis of molecular ozone, resulting from the reductions in overhead ozone. 

Human activity has also caused ozone changes, due to emissions of substances that deplete ozone in the stratosphere and precursors that generate ozone in the troposphere. The ozone changes, in particular in the troposphere, vary on regional scales. As discussed in WMO (1995 1999) and IPCC (1996) the radiative forcing due to ozone has a longwave as well as a shortwave component and there is a critical dependence on the vertical distribution of ozone changes. 

Nitrogen oxide (NOx) The result of photochemical reactions of nitric oxide in ambient air a major component of photochemical smog. It is a product of combustion from transportation and stationary sources and a major contributor to the formation of ozone in the troposphere and to acid deposition. 

Photochemical production of ozone in the troposphere occurs from the photolysis of nitrogen dioxide (N02) during the daytime, producing oxygen atoms (O) ... 

Crutzen PJ (1995) Ozone in the Troposphere, chapter in Singh HB (ed) Composition, Chemistry, and Climate of the Atmosphere. Van Nostrand Reinhold, New York... 

For a long time, transport from the stratosphere to the troposphere was thought to be the dominant source of ozone in the troposphere. Early in the 1970s, it was first suggested that tropospheric ozone originated mainly from production within the troposphere by photochemical oxidation of CO and hydrocarbons catalysed by HO and NO c- These sources are balanced by in-situ photochemical destruction of ozone and by dry deposition at the earth s surface. Many studies, both experimental- and model-based have set about determining the... 

From the preceding discussion of atmospheric photochemistry and NO chemistry, it can be seen that the fate of the peroxy radicals can have a marked effect on the ability of the atmosphere either to produce or to destroy ozone. Photolysis of NO2 and the subsequent reaction of the photoproducts with O2 (reactions (2.4) and (2.20)) are the only known way of producing ozone in the troposphere. In the presence of NO the following cycle for the production of ozone can take place ... 

Thus it should be clear that the question of tropospheric ozone is far from settled. The results of Mahlman would suggest that there is a net sink for ozone in the troposphere and that the net source is transport from the stratosphere while the results of Chameides... 

The movement of atmospheric constituents within a region and between regions is a key process in atmospheric chemistry. For example, the transport of chemicals from the troposphere to the stratosphere sets off the depletion of ozone. Conversely, the downward transport from the stratosphere increases ozone in the troposphere. The phenomenon that most distinguishes the troposphere from the stratosphere is the rate of vertical mixing. The time scale for the vertical transport of air and other chemical species in the troposphere can be of a few hours, whereas vertical transport in the stratosphere can last months or years. 

A homogeneous catalyst exists in the same phase as the reacting molecules. There are many examples in both the gas and liquid phases. One such example is the unusual catalytic behavior of nitric oxide toward ozone. In the troposphere, the part of the atmosphere closest to earth, nitric oxide catalyzes ozone production. However, in the upper atmosphere it catalyzes the decomposition of ozone. Both of these effects are unfortunate environmentally. 

Globally, the oxides of nitrogen, NO (nitric oxide), NO2 (nitrogen oxide), and N2O (nitrous oxide), are key species involved in the chemistry of the troposphere and stratosphere. NO and N2O are produced mostly by microbial soil activity, whereas biomass burning is also an important source of NO. Nitric oxide is a species involved in the photochemical production of ozone in the troposphere, is involved in the chemical produaion of nitric acid, and is an important component of acid precipitation. Nitrous oxide plays a key role in stratospheric ozone depletion and is an important greenhouse gas, with a global warming potential more than 200 times that of CO2. 

Sphere, and certainly globally integrated ozone in the troposphere has a component from the stratosphere, but when you get down to the ground that you are discussing, that is not a major contributor. 

The data presented have important implications in the behavior of tropospheric nonanthropogenic ozone, aerosol, and other trace constituents. Observational and experimental data have been reported by Rip-perton et al. 20) indicating the natural synthesis of ozone in the troposphere. Considering this study, the ubiquitous presence of various terpenes (21), isoprene (22), and oxides of nitrogen (20) suggest that some ozone is synthesized in the lower troposphere by the reaction NO2 + a-pinene + hv. Conversely, the destruction of ozone in the troposphere is partially ascribed to reactions with the terpenes and intermediates of the photochemical mixture. 

Appiying Concepts Explain why the following statement is true Ozone in the troposphere is considered a pollutant, but ozone in the stratosphere is essential for life on Earth. 

Reaction chain leading to the destruction of ozone in the troposphere (Crutzen, 1974)... 

Crutzen, P. J., 1974 Photochemical reactions by and influencing ozone in the troposphere. Tellus 26,... 

All in all, some 50 million to 60 million tons of SO2 are released into the atmosphere each year Some of it is oxidized to SO3. For example, it may react with ozone in the troposphere as follows ... 

---